1. Field of the Invention
This invention relates to mildew resistant paint compositions comprising isothiazolone compounds.
2. Description of the Prior Art
Isothiazolones are well known mildewcides for film forming compositions. Isothiazolones are generally unstable without the addition of a stabilizer. In aqueous paint formulations, copper nitrate is a well known stabilizer for isothiazolones.
U.S. Pat. Nos. 3,870,795 and 4,067,878 teach the stabilization of isothiazolones against chemical decomposition by addition of a metal nitrite or metal nitrate salts, but teach that other common metal salts, including carbonates, sulfates, chlorates, perchlorates, and chlorides are ineffective in stabilizing solutions of isothiazolones, such solutions usually being in water or in an hydroxylic solvent and immiscible with solvent-soluble isothiazolones. Salts of organic carboxylic acids of more than six carbon atoms with copper are not taught or considered in these patents.
U.S. Pat. Nos. 4,150,026 and 4,241,214 teach metal salt complexes of isothiazolones useful because of their enhanced thermal stability, while retaining biological activity. The metal salts listed do not include salts of organic carboxylic acids of more than six carbon atoms with copper, or complexes of copper with organic-soluble reagents.
U.S. Pat. No. 4,608,183 teaches synergistic biocidal mixture of isothiazolones and a metal complex with a polyfunctional ligand, requiring that the metal complex itself be a biocide. Illustrated specifically is the water-soluble cupric disodium citrate. It is known to use certain organic stabilizers for isothiazolones, generally for use situations where metal salts may create problems, such as corrosion, coagulation of latices, insolubility in non-aqueous media, interaction with the substrate to be stabilized, and the like. Formaldehyde or formaldehyde-releasing chemicals are known stabilizers, (see U.S. Pat. Nos. 4,165,318 and 4,129,448).
In certain applications, however, it is desirable to avoid addition of organic stabilizers by virtue of their volatility, decomposition under high heat, higher cost, difficulty in handling, potential toxicity, and the like. Formaldehyde is a suspected carcinogen, and it is desirable not to use formaldehyde or formaldehyde releasing chemicals in applications where contact with human skin or lungs may occur.
In actual use, copper salts of inorganic acids, such as copper (II) sulfate or nitrate, have proved efficacious in stabilization of isothiazolones. However, water-soluble inorganic copper salts are undesirable in effluent streams in such operations as in the manufacture of stabilized isothiazolones or in their blending into a product or the use of that product. Such water-soluble copper salts, especially the chlorides, may contribute to possible corrosion, or in the presence of polymers in aqueous dispersion may lead to coagulation of the dispersion. The water-soluble salts may not be readily miscible with certain of the water-insoluble isothiazolones, leading to separation and lowering of stability of a stabilizer concentrate.
Grove, U.S. Pat. No. 4,783,221 shows metal salts of organic carboxylic acids containing at least 6 carbon atoms wherein the metal is selected from the group consisting of copper and other transition metals, zinc, antimony, and lead, with an isothiazolone compound, and a solvent/diluent to preserve wood.